mod_firewall: Add checkcerts option for HTTP lists, cert verification disabled when SNI unsupported This provides a balance between security and usability. SNI is supported in Prosody trunk and in Prosody 0.11 from commit 30d3f6f85eb8 (scheduled for 0.11.7).

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.